1. Field of the Invention
The present invention provides a heat resistant fuel hose. More specifically, the present invention provides a heat resistant fuel hose having a rubber inner pipe in which vulcanized bonding of hydrogenated acrylonitrile butadiene rubber (H-NBR) and acrylic rubber (ACM) has been performed.
2. Description of the Related Art
In recent years, there has been a demand for fuel hoses with heat resistance and fuel resistance. For example, due to exhaust gas countermeasures, front wheel drive, and the like, the temperature inside the engine housing of automobiles has become more severe. Due to the advances of low fuel consumption, there has been a dramatic rise in the level of heat resistance demanded by the peripheral parts of diesel engines. As a result, diesel fuel hoses, for example, require high heat resistance at around 150° C. for 500 hours.
Methods of using acrylonitrile butadiene rubber (NBR) or acrylic rubber (ACM) in the inner pipe of the fuel hose do not always adequately satisfy the heat resistance and fuel resistance requirements. These methods are particularly inadequate for diesel fuel hoses. Adequate heat and fuel resistance is achieved by using fluorine rubber (FKM). However, FKM is very expensive, and there are problems with inadequate cold resistance and the inadequate workability of the non-vulcanized molded body.
On the other hand, of the nitrile rubbers, H-NBR in which the butadiene units of NBR are completely or partially hydrogenated has excellent heat resistance, fuel resistance, and cold resistance. . Although H-NBR is relatively expensive, the cost is more reasonable compared to FKM. By using the relatively expensive H-NBR in the inner layer of the inner pipe of the hose and by using an inexpensive rubber having some heat resistance and fuel resistance (such as ACM, preferably) for the outer layer of the inner pipe of the hose, the layer of H-NBR can be thinner. The amount of H-NBR is reduced, and this construction is more practical.
References such as Japanese Laid-Open Patent Publication No. 9-124845, Japanese Laid-Open Patent Publication No. 9-112756, and Japanese Laid-Open Patent Publication No. 2001-279021 disclose hoses using H-NBR mixtures and H-NBR mixtures for use in hoses and the like. In addition, Japanese Laid-Open Patent Publication No. 11-325332 discloses a hose having an innermost layer of H-NBR and an outer layer of ACM which is vulcanized and molded to form a unitary body.
When constructing a heat resistant fuel hose having a rubber inner pipe with an inner layer of H-NBR and an outer layer of ACM in the inner pipe, the inner layer in the inner pipe needs to be securely bonded with the outer layer in the inner pipe, preferably by vulcanized bonding. At the same time, it is preferable to improve the heat resistance of the rubber inner pipe as much as possible.
Japanese Laid-Open Patent Publication No. 9-124845, Japanese Laid-Open Patent Publication No. 9-112756, and Japanese Laid-Open Patent Publication No. 2001-279021 described above disclose ways to improve the H-NBR mixtures according to each of their technical objectives. Ways to improve heat resistance in general are also disclosed in these references. However, the references do not disclose ways to improve bonding between H-NBR and ACM while simultaneously improving the heat resistance of H-NBR.
Japanese Laid-Open Patent Publication No. 11-325332 described above discloses a hose having vulcanized bonding between the H-NBR layer and the ACM layer by peroxide vulcanization of H-NBR. The peroxide vulcanization is considered to be beneficial for improving the heat resistance of H-NBR. However, according to the research of the present inventors, the carboxyl group cross-linking type of ACM used in the disclosed invention does not always achieve strong vulcanized bonding with H-NBR. In addition, the method of peroxide vulcanization of H-NBR does not particularly improve the bonding of the two layers.
Furthermore, although the mixing of silica filler into H-NBR may improve the vulcanized bonding with ACM, the workability of the non-vulcanized molded body remains inadequate.